Fundamental quantum noise mapping with tunnelling microscopes tested at surface structures of subatomic lateral sizeElectronic supplementary information (ESI) available. See DOI: 10.1039/c3nr02216a

• Main Authors: Herz, Markus, Bouvron, Samuel, avar, Elizabeta, Fonin, Mikhail, Belzig, Wolfgang, Scheer, Elke
• Format: Article
• Language: English
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/c3nr02216a

We present a measurement scheme that enables quantitative detection of the shot noise in a scanning tunnelling microscope while scanning the sample. As test objects we study defect structures produced on an iridium single crystal at low temperatures. The defect structures appear in the constant current images as protrusions with curvature radii well below the atomic diameter. The measured power spectral density of the noise is very near to the quantum limit with Fano factor F = 1. While the constant current images show detailed structures expected for tunnelling involving d-atomic orbitals of Ir, we find the current noise to be without pronounced spatial variation as expected for shot noise arising from statistically independent events. Simultaneous high resolution imaging of topography and Fano factor around a tip-induced defect of subatomic size. While the topography signal shows a pronounced structure, the Fano factor mapping is featureless, confirming the tunneling nature of the electronic transport.